1. Field of the Invention
The invention relates to control devices for electromagnetic clutches.
2. Description of the Related Art
Conventionally, electromagnetic clutches are widely known in the art that are capable of permitting and cutting off torque transmission between a first rotary member and a second rotary member by controlling current application to an electromagnetic coil. See, e.g., Japanese Patent Application Publication No. 2009-138798 (JP 2009-138798 A). Even if power supply to the electromagnetic coil is stopped in order to cut off torque transmission between the first and second rotary members, a current flowing in the electromagnetic coil does not immediately become zero due to a back electromotive force that is generated due to electromagnetic induction so as to oppose a change in the amount of current flowing in the electromagnetic coil. This causes delay in response of the electromagnetic clutch.
As a solution to this problem, Japanese Patent Application Publication No. 2004-92691 (JP 2004-92691 A), for example, proposes a control device for an electromagnetic clutch in which a load such as a resistor is connected in parallel to an electromagnetic coil so that a current due to a back electromotive force flows in the load when power supply to the electromagnetic coil is stopped. The back electromotive force that is generated in the electromagnetic coil when power supply to the electromagnetic coil is stopped is consumed by conversion to heat in the load. Accordingly, a current flowing in the electromagnetic coil can quickly become zero, and responsiveness of the electromagnetic clutch can be improved.
In recent years, higher responsiveness has been required for the electromagnetic clutches, and the required level of responsiveness has not been achieved even with such a configuration as described in JP 2004-92691 A. Accordingly, there is a demand for a new technique capable of implementing higher responsiveness.